Material for fluorine-containing coating composition and method for coating by using same

ABSTRACT

To provide a fluorine-containing coating material which gives excellent adhesive strength directly to a substrate such as metal, glass, etc. with maintaining excellent characteristics of the fluorine-containing polymer such as thermal resistance, chemical resistance, non-sticking property and low friction property, and a method for coating the material. The fluorine-containing coating material is prepared by using a fluorine-containing ethylenic polymer having functional group which is obtained by copolymerizing (a-1) 0.05 to 30% by mole of at least one of fluorine-containing ethylenic monomers having any one of functional groups selected from hydroxyl, carboxyl, carboxylate salt group, carboxylate ester group or epoxy and (b-1) 70 to 99.95% by mole of at least one of fluorine-containing ethylenic monomers having no functional group mentioned above.

This application is the National Stage of International Application No.PCT/JP96/03575, filed Dec. 5, 1996.

TECHNICAL FIELD

The present invention relates to a material for a fluorine-containingcoating composition, a primer for a fluorine-containing coatingcomposition, an aqueous dispersion for a fluorine-containing coatingcomposition, a fluorine-containing powder coating composition and aresin composition for a fluorine-containing coating composition whichcan be firmly adhered to substrates such as metal, glass, etc. whencoating the substrate with a fluorine-containing polymer, and a methodfor coating a surface of a substrate with a fluorine-containing polymerby using the primer for a fluorine-containing coating composition.

BACKGROUND ART

A fluorine-containing polymer has been preferably used as a coatingmaterial applied to a surface of metal because of its excellentcharacteristics such as chemical resistance, thermal resistance andnon-sticking property, and is used, for example, for lining of chemicalapparatuses requiring corrosion resistance, inner lining of cookingapparatuses such as a rice cooker requiring corrosion resistance andnon-sticking property, and other applications. However since itsadhesion to a surface of metal is not sufficient due to its excellentnon-sticking property, hitherto various modifications have been made toimprove adhesion to the surface of metal.

One of them is a method for adhering a fluorine-containing polymer to asubstrate by roughening the surface of metal chemically or physicallywith expecting an "anchor effect" therebetween. In this method, thesurface roughening itself requires much labor, and though initialadhesion is possible, lowering of the anchor effect arises at the timeof temperature change and at high temperature.

Also a method for chemically activating a surface of afluorine-containing resin by treating the surface with a solutionprepared by dissolving metallic sodium in liquid ammonia has beenproposed. However, in this method, not only there was a fear that thesolution itself causes environmental pollution but also there was aproblem that its handling is attended with danger. Further, there havebeen proposed methods for carrying out physical and chemical treatmentsuch as plasma sputtering on a surface of a fluorine-containing resin ormechanically roughening the surface of a fluorine-containing resin.However these methods have problems such that the mentioned treatmentsrequire much labor, increase in cost arises and design or appearance ofa coated surface is injured.

Also in order to improve adhesion of a fluorine-containing coating,investigations with respect to addition of various components and use ofa primer have been made.

For example, there is a technique of adding an inorganic acid such aschromic acid to a coating composition containing a fluorine-containingpolymer to form a chemical conversion coating film on a surface of metalfor enhancing adhesion of the composition (JP-B-63-2675). However sincechromic acid contains hexahydric chromium, it can be said that such atechnique is not sufficient in view of safety in food and coating work.Further in case of use of other inorganic acids such as phosphoric acid,there was a problem such that safety of a fluorine-containing resincoating composition is damaged.

Use of a coating composition containing a fluorine-containing resin as aprimer, in which heat resistant resins such as polyamideimide,polyimide, polyethersulfone and PEEK and in addition, a metal powder areadded instead of the above-mentioned inorganic acid, has been studied(JP-A-6-264000). Inherently there is no compatibility between afluorine-containing polymer and heat resistant resin. Therefore therearises a phase separation in a coating film, thus easily causingintercoat adhesion failure between the primer and the top coat. Further,film defects such as pin holes and cracks arise easily at the time ofprocessing at high temperature and during use due to difference in heatshrinkage between the fluorine-containing resin and the heat resistantresin or due to lowering of elongation of the coating film by theaddition of the heat resistant resin. Also since these heat resistantresins are colored brown by baking, it is difficult to use them forapplications requiring white and vivid colors and transparency.

Further, non-sticking property and low friction property which thefluorine-containing resin inherently possesses are lowered.

Also for adhesion of a fluorine-containing resin coating composition toa glass requiring transparency, improvements of the adhesion have beentried by treating the substrate with a silane coupling agent or adding asilicone resin to the fluorine-containing resin coating composition(JP-B-54-42366, JP-A-5-177768, etc.). However thermal resistance andadhesion are insufficient, and separation of film, foaming and coloringarise easily at high temperature.

On the contrary, fluorine-containing coating compositions prepared bycopolymerizing a hydrocarbon monomer containing a functional group suchas hydroxyl or carboxyl have been discussed. However those coatingcompositions were originally studied mainly for a purpose of weatherresistance, and therefore it is difficult to use them for applicationsrequiring thermal resistance at 200° to 350° C. which is directed by thepresent invention, and for applications requiring non-sticking property,low friction property, etc.

Namely with respect to a polymer prepared by copolymerizing ahydrocarbon monomer (containing no fluorine) having a functional group,thermal decomposition easily occurs on components of the monomer at thetime of processing at high temperature or during use, and thus coatingfilm failure, coloring, foaming, separation, etc. arise, which makes itimpossible to attain purposes of coating a fluorine-containing resin.

An object of the present invention is to solve the above-mentionedproblems, and to provide a material for fluorine-containing coatingcomposition which maintains excellent characteristics such as thermalresistance, chemical resistance, non-sticking property and low frictionproperty of fluorine-containing polymer and further can have strongadhesion directly to a substrate such as metal, glass, etc., and toprovide a method for coating by using the material for coatingcompositions.

DISCLOSURE OF THE INVENTION

The present invention relates to a material for a fluorine-containingcoating composition which comprises a fluorine-containing ethylenicpolymer having a functional group and prepared by copolymerizing:

(a-1) 0.05 to 30% by mole of at least one of fluorine-containingethylenic monomers having any one of functional groups selected fromhydroxyl, carboxyl, carboxylate salt group, carboxylate ester group orepoxy and

(b-1) 70 to 99.95% by mole of at least one of fluorine-containingethylenic monomers which do not have the functional group mentionedabove.

Further the present invention relates to a primer for afluorine-containing coating composition which comprises afluorine-containing ethylenic polymer having a functional group andprepared by copolymerizing:

(a-2) 0.05 to 30% by mole of at least one of fluorine-containingethylenic monomers having any one of functional groups selected fromhydroxyl, carboxyl, carboxylate salt group, carboxylate ester group orepoxy and

(b-2) 70 to 99.95% by mole of at least one of fluorine-containingethylenic monomers which do not have the functional group mentionedabove.

Further the present invention relates to an aqueous dispersion for afluorine-containing coating composition which comprises afluorine-containing ethylenic polymer having a functional group andprepared by copolymerizing:

(a-3) 0.05 to 30% by mole of at least one of fluorine-containingethylenic monomers having any one of functional groups selected fromhydroxyl, carboxyl, carboxylate salt group, carboxylate ester group orepoxy and

(b-3) 70 to 99.95% by mole of at least one of fluorine-containingethylenic monomers which do not have the functional group mentionedabove.

Further the present invention relates to a fluorine-containing powdercoating composition which comprises a fluorine-containing ethylenicpolymer having functional group and prepared by copolymerizing:

(a-4) 0.05 to 30% by mole of at least one of fluorine-containingethylenic monomers having any one of functional groups selected fromhydroxyl, carboxyl, carboxylate salt group, carboxylate ester group orepoxy and

(b-4) 70 to 99.95% by mole of at least one of fluorine-containingethylenic monomers which do not have the functional group mentionedabove.

In the present invention, it is preferable that the above-mentionedfluorine-containing ethylenic monomer (a-1) having a functional group isa fluorine-containing ethylenic monomer having hydroxyl group.

It is also preferable in the present invention that the above-mentionedfluorine-containing ethylenic monomer (a-1) having a functional group isat least one of monomers represented by the formula (1):

    CX.sub.2 ═CX.sup.1 --R.sub.f --Y                       (1)

wherein Y is --CH₂ OH, --COOH, carboxylate salt group, carboxylate estergroup or epoxy, X and X¹ are the same or different and each is hydrogenatom or fluorine atom, R_(f) is a divalent alkylene group having 1 to 40carbon atoms, a fluorine-containing oxyalkylene group having 1 to 40carbon atoms, a fluorine-containing alkylene group having ether bond and1 to 40 carbon atoms or a fluorine-containing oxyalkylene group havingan ether bond and 1 to 40 carbon atoms.

It is also preferable in the present invention that in theabove-mentioned formula (1), Y is --CH₂ OH.

It is further preferable in the present invention that theabove-mentioned fluorine-containing ethylenic monomer (a-1) having afunctional group is a fluorine-containing monomer represented by theformula (2):

    CH.sub.2 ═CFCF.sub.2 --R.sub.f.sup.1 --Y.sup.1         (2)

wherein Y¹ is --CH₂ OH, --COOH, carboxylate salt group, carboxylateester group or epoxy, R_(f) ¹ is a divalent fluorine-containing alkylenegroup having 1 to 39 carbon atoms or --OR_(f) ², in which R_(f) ² is adivalent fluorine-containing alkylene group having 1 to 39 carbon atomsor a divalent fluorine-containing alkylene group having a ether bond and1 to 39 carbon atoms.

It is preferable in the present invention that the fluorine-containingethylenic monomer (b-1) having no functional group mentioned above istetrafluoroethylene.

It is preferable in the present invention that the fluorine-containingethylenic monomer (b-1) having no functional group mentioned above is amonomer mixture of 85 to 99.7% by mole of tetrafluoroethylene and 0.3 to15% by mole of a monomer represented by the formula (3):

    CF.sub.2 ═CF--R.sub.f.sup.3                            (3)

wherein R_(f) ³ is --CF₃ or OR_(f) ⁴, in which R_(f) ⁴ is aperfluoroalkyl group having 1 to 5 carbon atoms.

It is preferable in the present invention that the fluorine-containingethylenic monomer (b-1) having no functional group mentioned above is amonomer mixture of 40 to 80% by mole of tetrafluoroethylene orchlorotrifluoroethylene, 20 to 60% by mole of ethylene and 0 to 15% bymole of other monomer copolymerizable therewith.

Further the present invention relates to a resin composition for afluorine-containing coating composition which comprises:

(A-1) 1 to 90% by weight of a fluorine-containing ethylenic polymerhaving a functional group and prepared by copolymerizing:

(a-5) 0.05 to 30% by mole of at least one of fluorine-containingethylenic monomers having any one of functional groups selected fromhydroxyl, carboxyl, carboxylate salt group, carboxylate ester group orepoxy and

(b-5) 70 to 99.95% by mole of at least one of fluorine-containingethylenic monomers having no functional group mentioned above, and

(B-1) 10 to 99% by weight of a fluorine-containing ethylenic polymerhaving no functional group in its branched chain.

In the present invention, it is preferable that the above-mentionedfluorine-containing ethylenic polymer (A-1) having a functional group isat least one of fluorine-containing ethylenic polymers having afunctional group such as

a copolymer comprising (a-5) at least one of fluorine-containingethylenic monomers having functional group and represented by theformula (1):

    CX.sub.2 ═CX.sup.1 --R.sub.f --y                       (1)

wherein Y represents --CH₂ OH, --COOH, carboxylate salt group,carboxylate ester group or epoxy, X and X¹ are the same or different andeach is hydrogen atom or fluorine atom, R_(f) is a divalent alkylenegroup having 1 to 40 carbon atoms, a fluorine-containing oxyalkylenegroup having 1 to 40 carbon atoms, a fluorine-containing alkylene grouphaving an ether bond and 1 to 40 carbon atoms or a fluorine-containingoxyalkylene group having an ether bond and 1 to 40 carbon atoms, and

(b-5) tetrafluoroethylene, and a copolymer comprising theabove-mentioned fluorine-containing monomer (a-5) having a functionalgroup and as the component (b-5), a monomer mixture of 85 to 99.7% bymole of tetrafluoroethylene and 0.3 to 15% by mole of a monomerrepresented by the formula (3):

    CF.sub.2 ═CF--R.sub.f.sup.3                            (3)

wherein R_(f) ³ is --CF₃ or OR_(f) ⁴, in which R_(f) ⁴ is aperfluoroalkyl group having 1 to 5 carbon atoms, based on the totalamount of the monomers except the component (a-5), and that

(B-1) is at least one of polytetrafluoroethylene,tetrafluoroethylene-hexafluoropropylene copolymer ortetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer.

Further the present invention relates to the method for coating asurface of substrate with a fluorine-containing polymer, whichcomprises:

forming, on the substrate, a layer of a primer for a fluorine-containingcoating composition which comprises a fluorine-containing ethylenicpolymer (A-2) having a functional group and prepared by copolymerizing

(a-2) 0.05 to 30% by mole of at least one of fluorine-containingethylenic monomers having any one of hydroxyl, carboxyl, carboxylatesalt group, carboxylate ester group or epoxy and

(b-2) 70 to 99.95% by mole of at least one of fluorine-containingethylenic monomers having no functional group; forming, on the formedprimer layer, a layer of a fluorine-containing ethylenic polymer (B-1)having no functional group in its branched chain; and then sintering theprimer layer and the layer of the fluorine-containing ethylenic polymerhaving no functional group in its branched chain.

Further in the present invention, it is preferable that theabove-mentioned primer (A-2) for a fluorine-containing coatingcomposition is at least one of fluorine-containing ethylenic polymershaving a functional group such as

a copolymer comprising (a-2) at least one of the fluorine-containingethylenic monomer having a functional group and represented by theformula (1):

    CX.sub.2 ═CX.sub.1 --R.sub.f --Y                       (1)

wherein Y represents --CH₂ OH, --COOH, carboxylate salt group,carboxylate ester group or epoxy, X and X¹ are the same or different andeach is hydrogen atom or fluorine atom, R_(f) is a divalent alkylenegroup having 1 to 40 carbon atoms, a fluorine-containing oxyalkylenegroup having 1 to 40 carbon atoms, a fluorine-containing alkylene grouphaving ether bond and 1 to 40 carbon atoms or a fluorine-containingoxyalkylene group having ether bond and 1 to 40 carbon atoms, and

(b-2) tetrafluoroethylene, and a copolymer comprising (a-2) theabove-mentioned fluorine-containing monomer having a functional groupand as the component (b-2), a monomer mixture of 85 to 99.7% by mole oftetrafluoroethylene and 0.3 to 15% by mole of a monomer represented bythe formula (3):

    CF.sub.2 ═CF--R.sub.f.sup.3                            (3)

wherein R_(f) ³ is --CF₃ or OR_(f) ⁴, in which R_(f) ⁴ is aperfluoroalkyl group having 1 to 5 carbon atoms, based on the totalamount of the monomers except the component (a-2), and that

(B-2) is at least one of polytetrafluoroethylene,tetrafluoroethylene-hexafluoropropylene copolymer ortetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer.

Further it is preferable in the present invention that the surface of asubstrate to be coated with the above-mentioned fluorine-containingpolymer is a metal surface.

Further the present invention relates to the method for coating thesurface of glass substrate with any of the above-mentionedfluorine-containing polymers.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagrammatical plan view for explaining a coated sample madefor measuring adhesive strength in the Example of the present invention.

FIG. 2 is a diagrammatical perspective view of a measuring equipmentused for measuring adhesive strength in the Example of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

The fluorine-containing polymer used for the material forfluorine-containing coating composition, i.e. the fluorine-containingcoating material of the present invention is a fluorine-containingethylenic polymer having a functional group and prepared bycopolymerizing:

(a-1) 0.05 to 30% by mole of at least one of fluorine-containingethylenic monomers having any one of functional groups selected fromhydroxyl, carboxyl, carboxylate salt group, carboxylate ester group orepoxy, and

(b-1) 70 to 99.95% by mole of at least one of fluorine-containingethylenic monomers having no functional group mentioned above.

In the present specification, the material for coating compositionincludes, for example, a primer, aqueous dispersion, resin compositionfor coating, or powder coating composition.

The present inventors have found that the above-mentionedfluorine-containing polymer having a functional group has a surprisinglystrong adhesive property to a substrate such as metal, glass or othermaterial even without surface-treating the substrate, applying a primerlayer or adding a component to enhance adhesive property of the coatingcomposition.

In the fluorine-containing coating material of the present invention, itis important to introduce a functional group into thefluorine-containing polymer by copolymerizing the above-mentionedfluorine-containing ethylenic monomer (a-1) having a functional groupwith the fluorine-containing ethylenic monomer (b-1) having nofunctional group mentioned above. Thus the coating material can exhibitexcellent adhesion directly to the surfaces of various substrates, whichhas been hitherto insufficient or impossible. Namely as compared with afluorine-containing polymer having a functional group introduced bycopolymerizing with a non-fluorine-containing monomer having afunctional group, the fluorine-containing polymer having functionalgroup of the present invention is excellent in thermal resistance,exhibits more inhibited thermal decomposition at processing at hightemperature (for example, 200° to 400° C.), can give large adhesionforce and can form a coating film being free from coloring and foamingand pin holes, leveling failure, etc. Also when a coated article is usedat high temperature, the adhesion is maintained, and coating filmfailure such as coloring, whitening, foaming and pin holes hardly arise.

The above-mentioned fluorine-containing polymer having a functionalgroup, which is used as the fluorine-containing coating material of thepresent invention, has excellent characteristics including not onlythermal resistance but also chemical resistance, non-sticking property,low friction property and weather resistance which fluorine-containingpolymers possess. Those excellent characteristics of thefluorine-containing polymers are given to a surface of the coating filmafter coating without being lowered.

The functional group of the fluorine-containing ethylenic polymer havinga functional group, which is used for the fluorine-containing coatingmaterial of the present invention, is selected from hydroxyl, carboxyl,carboxylate salt group and carboxylate ester group. Adhesion to varioussubstrates can be given by an effect of the functional group. Thefunctional group is selected properly depending on kind, purpose andapplication of a surface of substrate. From the viewpoint of thermalresistance, the polymer having hydroxyl is preferable.

The fluorine-containing ethylenic polymer used for the coating materialof the present invention is a fluorine-containing ethylenic polymerprepared by copolymerizing

(a-1) 0.05 to 30% by mole of the fluorine-containing ethylenic monomerhaving functional group and represented by the formula (1):

    CX.sub.2 ═CX.sup.1 --R.sub.f --Y                       (1)

wherein X, X¹, R_(f) and Y are the same as in the above-mentionedformula (1), and

(b-1) 70 to 99.95% by mole of the fluorine-containing ethylenic monomerhaving no functional group mentioned above and being copolymerizablewith the component (a-1).

Examples of the fluorine-containing ethylenic monomer (a-1) having afunctional group are: ones represented by the formula (4):

    CF.sub.2 ═CF--R.sub.f.sup.5 --Y (4)

wherein Y is the same as in the formula (1), R_(f) ⁵ is a divalentfluorine-containing alkylene group having 1 to 40 carbon atoms or--OR_(f) ⁶, in which R_(f) ⁶ is a divalent fluorine-containing alkylenegroup having 1 to 40 carbon atoms or a divalent fluorine-containingalkylene group having ether bond and 1 to 40 carbon atoms, onesrepresented by the formula (5):

    CF.sub.2 ═CFCF.sub.2 --OR.sub.f.sup.7 --Y              (5)

wherein Y is the same as in the formula (1), --R_(f) ⁷ is a divalentfluorine-containing alkylene group having 1 to 39 carbon atoms or adivalent fluorine-containing alkylene group having ether bond and 1 to39 carbon atoms, one represented by the formula (2):

    CH.sub.2 ═CFCF.sub.2 --R.sub.f.sup.1 --Y.sup.1         (2)

wherein Y¹ is the same as in the formula (1), --R_(f) ¹ is a divalentfluorine-containing alkylene group having 1 to 39 carbon atoms or--OR_(f) ², in which R_(f) ² is a divalent fluorine-containing alkylenegroup having 1 to 39 carbon atoms or a divalent alkylene group having anether bond and 1 to 39 carbon atoms, and

ones represented by the formula (6):

    CH.sub.2 ═CH--R.sub.f.sup.8 --Y                        (6)

wherein Y is the same as in the formula (1), and R_(f) ⁸ is a divalentfluorine-containing alkylene group having 1 to 40 carbon atoms.

The fluorine-containing ethylenic monomers having functional group andrepresented by the formulae (2) and (4) to (6) are preferable from thepoints that copolymerizability thereof with the fluorine-containingethylenic monomer (b-1) is relatively good and that thermal resistanceof the polymer obtained by copolymerizing is not lowered remarkably.

Among them, from the viewpoints of copolymerizability with otherfluorine-containing ethylenic monomers and thermal resistance of theobtained polymer, the compounds of the formulae (4) and (2) arepreferable and the compound of the formula (2) is particularlypreferable.

Examples of the fluorine-containing monomer (4) having a functionalgroup are:

CF₂ ═CFOCF₂ CF₂ CH₂ OH, CF₂ ═CFO(CF₂)₃ COOH, CF₂ ═CFOCF₂ CF₂ COOCH₃,##STR1## CF₂ ═CFCF₂ COOH, CF₂ ═CFCF₂ CH₂ OH, ##STR2## and the like.Examples of the fluorine-containing monomer (5) having a functionalgroup are:

CF₂ ═CFCF₂ OCF₂ CF₂ CF₂ COOH, ##STR3## and the like. Examples of thefluorine-containing monomer (2) having a functional group are:

CH₂ ═CFCF₂ CF₂ CH₂ CH₂ OH, CH₂ ═CFCF₂ CF₂ COOH, ##STR4## and the like.

Examples of the fluorine-containing monomer (6) having a functionalgroup are:

CH₂ ═CHCF₂ CF₂ CH₂ CH₂ COOH, ##STR5## and the like.

Examples of the other fluorine-containing monomer are: ##STR6## and thelike.

The ethylenically unsaturated monomer copolymerizable with thefluorine-containing ethylenically unsaturated monomer (a-1) having afunctional group can be selected optionally from known monomers. Inorder to give thermal resistance, chemical resistance, non-stickingproperty and low friction property to copolymer, the copolymerizableethylenic monomer is selected from fluorine-containing ethylenicmonomers.

Examples of the fluorine-containing ethylenic monomer are, for instance,tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene,vinylidene fluoride, vinyl fluoride, perfluoro(alkyl vinyl ethers),hexafluoroisobutene, ##STR7## wherein both X are selected from H, Cl andP, both of n are an integer of 1 to 5, and the like.

Also in addition to (a-1) and the above-mentioned fluorine-containingethylenic monomer, a non-fluorine-containing ethylenic monomer may becopolymerized in an amount not lowering thermal resistance andnon-sticking property. In that case, it is preferable that thenon-fluorine-containing ethylenic monomer is selected from ethylenicmonomers having 5 or less carbon atoms in order not to lower thermalresistance. Examples thereof are ethylene, propylene, 1-butene, 2-buteneand the like.

A content of functional groups in the fluorine-containing ethylenicpolymer having a functional group which is used for the coating materialof the present invention is from 0.05 to 30% by mole on the basis of thetotal amount of the monomers in the polymer. The content of functionalgroups is optionally selected depending on kind and shape of asubstrate, and coating method, conditions, purpose and application.Preferable content is from 0.05 to 20% by mole, particularly preferablyfrom 0.1 to 10% by mole.

When the content of the functional groups is less than 0.05%, sufficientadhesion to the surface of substrate is hardly obtained and separationof the coating film easily occurs due to temperature change andpenetration of chemicals. When more than 30% by mole, thermal resistanceis lowered, and at sintering at high temperature or during use at hightemperature, there easily occur adhesion failure, coloring, rupture of acoating film such as foaming and pin hole, separation of coating,elution, etc.

Examples of the preferable fluorine-containing polymer used for thefluorine-containing coating material of the present invention are:

a copolymer comprising 0.05 to 30% by mole of the fluorine-containingethylenic monomer (a-1) having a functional group and 70 to 99.95% bymole of tetrafluoroethylene (so-called polytetrafluoroethylene having afunctional group (functional group-containing PTFE));

a copolymer comprising 0.05 to 30% by mole of the fluorine-containingethylenic monomer (a-1) based on the total amount of monomers, andfurther 85 to 99.7% by mole of tetrafluoroethylene and 0.3 to 15% bymole of the monomer represented by the formula (3):

    CF.sub.2 ═CF--R.sub.f.sup.3                            (3)

wherein R_(f) ³ is selected from --CF₃ and OR_(f) ⁴, in which R_(f) ⁴ isa perfluoroalkyl group having 1 to 5 carbon atoms, based on the totalamount of monomers except the monomer (a-1) (functional group-containingtetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer (functionalgroup-containing PFA) or functional group-containingtetrafluoroethylene-hexafluoropropylene copolymer (functionalgroup-containing FEP));

a copolymer comprising 0.05 to 30% by mole of the fluorine-containingethylenic monomer (a-1) based on the total amount of monomers, andfurther 40 to 80% by mole of tetrafluoroethylene, 20 to 60% by mole ofethylene and 0.15% by mole of other copolymerizable monomer, based onthe total amount of monomers except the monomer (a-1) (functionalgroup-containing ethylene-tetrafluoroethylene copolymer (functionalgroup-containing ETFE); and the like.

Examples of the other copolymerizable monomer used forethylene-tetrafluoroethylene (or chlorotrifluoroethylene) copolymerhaving hydroxyl are hexafluoropropylene, hexafluoroisobutene, CH₂═CF--(--CF₂ --)_(n) --X, CH₂ ═CH--(--CF₂ --)--X, wherein X is H, Cl orF, n is an integer of 1 to 5, perfluoro(alkyl vinyl ethers) and thelike.

Those exemplified fluorine-containing ethylenic polymers are preferablein that they are excellent particulary in thermal resistance, chemicalresistance, non-sticking property and low friction property amongfluorine-containing polymers. While the above exemplifiedfluorine-containing polymers (PTFE, PFA, FEP, ETFE) having no functionalgroup have excellent characteristics mentioned above, they are materialshaving the lowest adhesive property to the surface of substrate, and aresuitably demanded to improve adhesive property and coating to varioussubstrates.

The fluorine-containing polymer having a functional group which is usedfor the fluorine-containing coating material of the present inventioncan be prepared by copolymerizing the above-mentionedfluorine-containing ethylenic monomer (a-1) having a functional groupand fluorine-containing ethylenic monomer (b-1) through knownpolymerization methods. Among them, radical polymerization method isemployed mainly. Namely means for initiating the polymerization is notlimited so as to initiate the polymerization radically. For example, thepolymerization is initiated with an organic or inorganic radicalinitiator, heat, light or ionizing radiation. The polymerization can becarried out by solution polymerization, bulk polymerization, suspensionpolymerization, emulsion polymerization, etc. A molecular weight isregulated by concentration of the monomers to be polymerized,concentration of the initiator, concentration of a chain transfer agentand polymerization temperature. A composition of the copolymer to beproduced can be controlled by kinds and amounts of monomers used.

To the fluorine-containing coating material of the present invention canbe added a pigment, surfactant, viscosity control agent, levellingagent, thermal stabilizer, etc. which are usually used for coatingcompositions, to the extent of not lowering thermal resistance, chemicalresistance and non-sticking property of the fluorine-containing resin.

The fluorine-containing ethylenic polymer having functional group whichis used for the fluorine-containing coating material of the presentinvention can be used as a primer, by utilizing its adhesive force, fora fluorine-containing coating composition having good thermal resistancewhen coating a surface of metal or glass substrate with afluorine-containing resin.

The fluorine-containing primer of the present invention comprises afluorine-containing ethylenic polymer having functional group andprepared by copolymerizing:

(a-2) 0.05 to 30% by mole of at least one of fluorine-containingethylenic monomers having any one of hydroxyl, carboxyl, carboxylatesalt group, carboxylate ester group or epoxy and

(b-2) 70 to 99.95% by mole of at least one of fluorine-containingethylenic monomers having no functional group.

As the fluorine-containing primer of the present invention, there can beused the same ones as the fluorine-containing coating material of thepresent invention. The fluorine-containing primer is optionally selecteddepending on kind of substrate surface, kind of fluorine-containingpolymer (kind of top coat) to be coated on the substrate through theprimer, etc. In general preferable primer for fluorine-containingcoating composition is one which has the same structure as thefluorine-containing polymer to be coated thereon and contains afunctional group.

This combination exhibits good compatibility between thefluorine-containing polymer used for the primer and thefluorine-containing polymer to be coated on the primer and gives notonly good adhesion between the primer and the substrate but also goodintercoat adhesion between the primer layer and the top coat layer. Evenin case of use at high temperature, intercoat adhesion failure,cracking, pin hole, etc. due to difference in thermal shrinkage ofpolymers hardly occur unlike a primer which contains other resins. Alsosince the whole coating film is composed of the fluorine-containingpolymer, the film has transparency and vivid coloring and can be goodenough for applications requiring good appearance of design. Further,excellent thermal resistance, chemical resistance, non-sticking propertyand low friction property can be exhibited more effectively, since thelayer of fluorine-containing polymer having no functional group isformed on the outermost surface of the coating film.

As the primer of the present invention for fluorine-containing coatingcomposition, there can be used the same ones as the fluorine-containingcoating material of the present invention. When coating a surface of asubstrate with PTFE, it is preferable to use any one selected from thecoating materials of claims 9 and 10 (functional group-containing PTFE,PFA, FEP) as the primer. Particularly the use of the thermoprocessingcoating material of claim 10 (functional group-containing PFA or FEP) asthe primer is more preferable in that they can be adhered strongly tothe surface of substrate through thermally melting by sintering. Whencoating a surface of substrate with PFA or FEP, it is preferable to usethe coating materials of claim 10 (functional group-containing PFA orFEP) as the primer.

The fluorine-containing coating material of the present invention iscapable of being in the form of an aqueous dispersion, organic solventdispersion, powder, particle, organosol, organosol emulsion in water,etc. Among them, an aqueous dispersion or powder is preferably used fromenvironmental and safety points of view.

The aqueous dispersion of the present invention for fluorine-containingcoating composition comprises a fluorine-containing ethylenic polymer ahaving functional group and prepared by copolymerizing:

(a-3) 0.05 to 30% by mole of at least one of fluorine-containingethylenic monomers having any one of functional groups selected fromhydroxyl, carboxyl, carboxylate salt group, carboxylate ester group orepoxy, and

(b-3) 70 to 99.95% by mole of at least one of fluorine-containingethylenic monomers having no functional group mentioned above. Theaqueous dispersion for fluorine-containing coating composition isparticularly in a state of 0.01 to 1.0 μm fine particles of theabove-mentioned polymer being dispersed in water, and usually comprisesa composition containing a surfactant for stabilizing the dispersion. Tothe aqueous dispersion of the present invention can be added additivessuch as pigment, surfactant, defoaming agent, viscosity control agent,levelling agent, etc. which are usually used, in amounts not loweringremarkably thermal resistance, chemical resistance, non-stickingproperty and low friction property.

As the fluorine-containing polymer having a functional group which isused for the aqueous dispersion of the present invention, there areexemplified the same polymers as those for the above-mentionedfluorine-containing coating material.

Examples thereof are preferably aqueous dispersions of PTFE havingfunctional group (coating material of claim 9) and PFA having functionalgroup or FEP having functional group (coating material of claim 10).

The aqueous dispersion of the present invention can be prepared throughvarious methods, for example, a method wherein a powder of thefluorine-containing polymer having a functional group prepared bysuspension polymerization is finely pulverized and then the pulverizedpowder is dispersed homogeneously into an aqueous dispersion medium witha surfactant, a method wherein a fluorine-containing aqueous dispersionis prepared at the same time of polymerization by emulsionpolymerization and then a surfactant and additives are added as the casedemands, and other methods. From the viewpoints of productivity andquality (for making particle size small and uniform), a method ofpreparing an aqueous dispersion directly by emulsion polymerization ispreferred.

The powder coating composition of the present invention comprises afluorine-containing ethylenic polymer having a functional group andprepared by copolymerizing:

(a-4) 0.05 to 30% by mole of at least one of fluorine-containingethylenic monomers having any one of functional groups selected fromhydroxyl, carboxyl, carboxylate salt group, carboxylate ester group orepoxy, and

(b-4) 70 to 99.95% by mole of at least one of fluorine-containingethylenic monomers having no functional group mentioned above.

The fluorine-containing powder coating composition of the presentinvention is preferably being in the form of powder or granule having aparticle size of 10 to 1,000 μm and an apparent density of 0.2 to 1.2g/cc.

To the fluorine-containing powder coating composition of the presentinvention can be added optionally additives, for example, pigment suchas carbon powder, titanium oxide or cobalt oxide; reinforcement such asglass fiber powder, carbon fiber powder or mica; amine anti-oxidant;organic sulfur compound; organotin anti-oxidant; phenolic anti-oxidant;thermal stabilizer such as metal soap; levelling agent; anti-staticagent; etc., in amounts not lowering remarkably characteristics such asthermal resistance of the fluorine-containing resin.

The fluorine-containing powder coating composition of the presentinvention and the additives may be admixed in the form of powder (dry)or in the form of slurry (wet), and the mixing in the form of powder ispreferable. As the mixing equipment, there can be used a conventionalmixer or pulverizer, for example, a sand mill, V blender, ribbon blenderor the like.

The fluorine-containing powder coating composition of the presentinvention is in general coated by electrostatic spray coating,fluidized-bed dip coating, rotolining, etc., and then sintered to give agood coating film.

In general, in case of electrostatic powder spray coating, a coatingfilm having a thickness of 10 to 2,000 μm is formed, and in case ofrotolining, a coating film having a thickness of 200 to 10,000 μm isformed.

As the fluorine-containing polymer used for the fluorine-containingpowder coating composition of the present invention, there can be usedpreferably the same ones as the above-mentioned fluorine-containingcoating material. Example of the fluorine-containing powder coatingcomposition may be one comprising a coating material. Particularlypreferable are PTFE having a functional group, PFA having a functionalgroup, FEP having a functional group and ETFE having a functional group.

The fluorine-containing coating material of the present invention may beadmixed with a fluorine-containing polymer having no functional group inits branched chain, and thus can be prepared into a resin compositionfor fluorine-containing coating composition. By applying the obtainedcomposition, a coating film having good adhesion to surfaces of varioussubstrates can be obtained.

The fluorine-containing resin composition of the present invention is aresin composition for fluorine-containing coating composition whichcomprises:

(A-1) 1 to 90% by weight of a fluorine-containing ethylenic polymerhaving a functional group and prepared by copolymerizing:

(a-5) 0.05 to 30% by mole of at least one of fluorine-containingethylenic monomers having any one of functional groups selected fromhydroxyl, carboxyl, carboxylate salt group, carboxylate ester group orepoxy and

(b-5) 70 to 99.95% by mole of at least one of fluorine-containingethylenic monomers having no functional group mentioned above, and

(B-1) 10 to 99% by weight of a fluorine-containing ethylenic polymerhaving no functional group in its branched chain.

Example of the preferable fluorine-containing resin composition is aresin composition for a fluorine-containing coating composition,wherein:

the fluorine-containing ethylenic polymer (A-1) having a functionalgroup is at least one of fluorine-containing ethylenic polymers having afunctional group selected from a copolymer of

(a-5) at least one of fluorine-containing ethylenic monomers having afunctional group and represented by the formula (1):

    CX.sub.2 ═CX.sup.1 --R.sub.f --Y                       (1)

in which Y is --CH₂ OH, --COOH, carboxylate salt group, carboxylateester group or epoxy, X and X¹ are the same or different and each ishydrogen atom or fluorine atom, R_(f) is a divalent alkylene grouphaving 1 to 40 carbon atoms, a fluorine-containing oxyalkylene grouphaving 1 to 40 carbon atoms, a fluorine-containing alkylene group havingether bond and 1 to 40 carbon atoms or a fluorine-containing oxyalkylenegroup having ether bond and 1 to 40 carbon atoms and

(b-5) tetrafluoroethylene, and a copolymer of

(a-5) the above-mentioned fluorine-containing monomer having afunctional group and

(b-5) a monomer mixture of 85 to 99.7% by mole of tetrafluoroethyleneand 0.3 to 15% by mole of a monomer represented by the formula (3):

    CF.sub.2 ═CF--R.sub.f.sup.3                            (3)

wherein R_(f) ³ is --CF₃ or OR_(f) ⁴, in which R_(f) ⁴ is aperfluoroalkyl group having 1 to 5 carbon atoms, and (B-1) is at leastone of polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylenecopolymer or tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer.

This composition comprises a good combination of (A-1) and (B-1) whichare compatible with each other, and when coated, can give not only goodadhesion to the surface of substrate but also a coating film having hightransparency and vivid color in compliance with applications.

Also the inherent characteristics such as thermal resistance, chemicalresistance, non-sticking property and low friction property offluorine-containing resin are easily exhibited effectively.

The resin composition for fluorine-containing coating composition of thepresent invention can be in the form of aqueous dispersion, organicsolvent dispersion, powder, granule, organosol, aqueous organosolemulsion, etc. as mentioned above.

To the resin composition can be added pigment, surfactant, viscositycontrol agent, levelling agent, thermal stabilizer, etc. which areusually used for a coating composition, in amounts not loweringremarkably performance of the fluorine-containing polymer.

The present invention further relates to a method for coating a surfaceof a substrate with a fluorine-containing polymer, which comprises:forming, on a surface of a substrate, a layer of a primer (A-2) for afluorine-containing coating composition which comprises afluorine-containing ethylenic polymer having a functional group andprepared by copolymerizing

(a-2) 0.05 to 30% by mole of at least one of fluorine-containingethylenic monomers having any one of functional groups selected fromhydroxyl, carboxyl, carboxylate salt group, carboxylate ester group orepoxy, and

(b-2) 70 to 99.95% by mole of at least one of fluorine-containingethylenic monomers having no functional group mentioned above;

forming a layer of a fluorine-containing ethylenic polymer (B-1) havingno functional group in its branched chain, on the formed primer layer;and

sintering the primer layer and the layer of a fluorine-containingethylenic polymer having no functional group in its branched chain.

The method for coating with the fluorine-containing polymer of thepresent invention comprises mainly the following three steps:

(First step) a step for applying, to a surface of a substrate, theprimer for fluorine-containing coating composition of claim 2 whichcomprises the fluorine-containing polymer having a functional group,

(Second step) a step for applying the fluorine-containing coatingcomposition comprising the fluorine-containing polymer having nofunctional group, to the primer layer formed in the first step, and

(Third step) a step for sintering the coated layers formed in the firstand second steps.

Further, the primer layer applied in the first step may be set by dryingat 80° to 150° C. for about 5 minutes to about 30 minutes prior to thesecond step (2 coats/1 bake), and may be sintered, for example, at atemperature higher than the melting temperature thereof prior to thesecond step (2 coats/2 bakes).

The method for applying the primer in the first step is optionallyselected depending on the form of the primer. For example, in case wherethe fluorine-containing primer is in the form of an aqueous dispersion,there are employed spray coating, spin coating, brush coating and dipcoating methods. In case of the form of powder coating composition,there are used electrostatic coating, fluid-bed dip coating androtolining methods.

A thickness of the primer layer may vary depending on purpose,application, kind of a surface of the substrate and coating method. Thethickness is from 1 to 50 μm, preferably from 2 to 20 μm. Since thethickness of the primer is in general thin as mentioned above, it ispreferable to coat the primer in the form of an aqueous dispersion byspray coating, etc.

The method for applying the coating composition comprising thefluorine-containing polymer having no functional group to the primerlayer in the second step is optionally selected depending on the kind ofthe fluorine-containing polymer, form of the coating, purpose andapplication. For example, in case of an aqueous dispersion and organicsolvent dispersion, in general spray coating, brush coating, rollcoating and spin coating are used. In case of a powder coatingcomposition, electrostatic coating, fluid-bed dip coating and rotoliningare carried out.

A coating thickness of the fluorine-containing polymer in this stepvaries largely depending on purpose, application and coating method. Thethickness is in general from 5 to 50 μm, preferably from about 10 μm toabout 30 μm by spray coating. When a thick coating film is desired byusing a powder coating composition, it is possible to apply at 20 to2,000 μm thick by electrostatic coating and at 0.3 to 10 mm thick byrotolining.

Sintering conditions in the third step are optionally selected dependingon kinds of the fluorine-containing polymers (component, melting point,etc.) of the primer layer and top layer. In general the sintering iscarried out at a temperature of not less than the melting points of theboth fluorine-containing polymers. Sintering time is from five minutesto three hours, preferably from about 10 minutes to about 30 minutes,though it depends on the sintering temperature. For example, whencoating with PTFE, PFA and FEP, the sintering temperature is from 300°to 400° C., preferably from 320° to 400° C.

In the method for coating with the fluorine-containing polymer of thepresent invention, it is important to use the above-mentionedfluorine-containing polymer having a functional group as the primer.Thereby it becomes possible to coat surfaces of various substrates withthe fluorine-containing polymer though adhesion therebetween has beendifficult hitherto. Also particularly as the fluorine-containing polymerhaving a functional group which is used as the primer layer, it ispreferable to have the same components as those of thefluorine-containing polymer used for the top layer, and to which afunctional group is introduced.

Among the fluorine-containing polymers, for example, PTFE, PFE and FEPare most excellent in thermal resistance, chemical resistance,non-sticking property and low friction property, and coating therewithsurfaces of various substrates are demanded. When coating with thesefluorine-containing resins, it is preferable to use a primer comprisingat least one of polymers selected from PTFE having a functional group,PFA having a functional group and FEP having a functional group.

The fluorine-containing polymer can be applied, by the above-mentionedcoating method, to surfaces of various substrates, for example, metallicmaterials such as iron, aluminum, copper, tin, zinc, stainless steel,brass and aluminum alloy; inorganic materials such as glass,earthenware, concrete and silicon; organic materials such as fiber,paper, wood, leather, synthetic resin (particularly heat resistiveresins such as polyamide and PEEK, heat resistive engineering plastics,etc.) and synthetic rubber; etc.

In the coating method of the present invention, in order to furtherenhance adhesion of the fluorine-containing primer to the surface ofsubstrate, the substrate may be subjected to surface-treating by sandblasting, shot blasting, grit blasting, horning, paper scratching, wirescratching, hairline finishing, chemical treatment, plating,electrochemical treatment, chemical etching, etc.

EXAMPLE

The present invention is then explained in detail based on ReferenceExamples and Examples, but is not limited to them.

Reference Example 1

(Preparation of aqueous dispersion comprising PFA having hydroxyl)

A 3-liter glass-lined autoclave equipped with a stirrer, valve, pressuregauge and thermometer was charged with 1,500 ml of pure water and 9.0 gof ammonium perfluorooctanate. After replacing with nitrogen gassufficiently, the autoclave was evacuated and charged with 20 ml ofethane gas.

Then 3.8 g ofperfluoro-(1,1,9,9-tetrahydro-2,5-bistrifluoromethyl-3,6-dioxa-8-nonenol)(formula (7)): ##STR8## and 18 g of perfluoro(propyl vinyl ether) (PPVE)were fed into the autoclave with pressurized nitrogen gas, and atemperature inside the system was maintained at 70° C.

Pressurized tetrafluoroethylene (TFE) gas was introduced into theautoclave with stirring so that the inside pressure became 8.5 kgf/cm²G.

Then a solution prepared by dissolving 0.15 g of ammonium persulfate in5.0 g of water was fed with pressurized nitrogen gas to initiate thereaction.

Since the pressure lowered with the advance of the polymerizationreaction, at the time when the pressure lowered down to 7.5 kgf/cm² G,it was increased again to 8.5 kgf/cm² by feeding tetrafluoroethylenegas, and the decreasing and increasing of the pressure were repeated.

With continuing supply of tetrafluoroethylene, every time when about 40g of tetrafluoroethylene gas was consumed after starting of thepolymerization, 1.9 g of the fluorine-containing ethylenic monomerhaving hydroxyl (compound represented by the formula (7)) was introducedunder pressure three times (5.7 g in total) to continue thepolymerization. When about 160 g of tetrafluoroethylene was consumedafter starting of the polymerization, the supplying thereof wasterminated. The autoclave was cooled and the un-reacted monomer wasreleased to give 1,702 g of a bluish semitransparent aqueous dispersion.

A concentration of the polymer in the obtained aqueous dispersion was10.9%, and a particle size measured by dynamic light scattering methodwas 70.7 nm.

Also a part of the obtained aqueous dispersion was sampled and subjectedto freeze coagulation, and the precipitated polymer was rinsed and driedto isolate a white solid. Components and their amounts of the obtainedcopolymer which were determined through ¹⁹ F-NMR and IR analyses wereTFE/PPVE/(Fluorine-containing ethylenic monomer having hydroxyl andrepresented by the formula (7))=97.7/1.2/1.1% by mole.

In infrared spectrum, characteristic absorption of --OH was observed at3,620 to 3,400 cm⁻¹.

According to DSC analysis Tm was 310° C., and according to DTGA analysis1% thermal decomposition temperature Td was 368° C. A melt flow ratemeasured under conditions of preheating at 372° C. for five minutes at aload of 7 kgf/cm² by using Koka-type flow tester and nozzles of 2 mmφ×8mm length was 12.0 g/10 min.

Reference Example 2

(Preparation of aqueous dispersion of PFA having hydroxyl)

The same autoclave as in Reference Example was charged with 1,500 ml ofpure water and 9.0 g of ammonium perfluorooctanate. After replacing withnitrogen gas sufficiently, the autoclave was evacuated and charged with20 ml of ethane gas.

Then 1.9 g ofperfluoro-(1,1,9,9-tetrahydro-2,5-bistrifluoromethyl-3,6-dioxa-8-nonenol)(compound of the formula (7)) and 16.1 g of perfluoro(propyl vinylether) (PPVE) were fed into the autoclave with pressurized nitrogen gas,and a temperature inside the system was maintained at 70° C.

Pressurized tetrafluoroethylene (TFE) gas was introduced into theautoclave with stirring so that the inside pressure became 8.5 kgf/cm²G.

Then a solution prepared by dissolving 0.15 g of ammonium persulfate in5.0 g of water was fed with pressurized nitrogen gas to initiate thereaction.

Since the pressure lowered with the advance of the polymerizationreaction, at the time when the pressure lowered down to 7.5 kgf/cm² G,it was increased again to 8.5 kgf/cm² G by feeding tetrafluoroethylenegas, and the decreasing and increasing of the pressure were repeated.

With continuing supply of tetrafluoroethylene, every time when about 40g of tetrafluoroethylene gas was consumed after starting of thepolymerization, 0.95 g of the fluorine-containing ethylenic monomerhaving hydroxyl (compound represented by the formula (7)) was introducedunder pressure three times (2.85 g in total) to continue thepolymerization. When about 160 g of tetrafluoroethylene was consumedafter starting of the polymerization, the supplying thereof wasterminated. The autoclave was cooled and the un-reacted monomer wasreleased to give 1,692 g of an aqueous dispersion. A concentration ofthe polymer in the obtained aqueous dispersion was 10.6%, and a particlesize was 76.8 nm.

Also a part of the obtained aqueous dispersion was sampled, and a whitesolid was isolated in the same manner as in Reference Example 1.

Analysis of the obtained white solid indicates:

TFE/PPVE/(Fluorine-containing monomer having hydroxyl and represented bythe formula (7))=98.3/1.1/0.6% by mole Tm=310° C. 1% Thermaldecomposition temperature Td=374° C. Melt flow rate: 9.5 g/10 min

In infrared spectrum, characteristic absorption of --OH was observed at3,620 to 3,400 cm⁻¹.

Reference Example 3

(Synthesis of aqueous dispersion of PFA having no functional group)

Emulsion polymerization was carried out in the same manner as inReference Example 1 except thatperfluoro-(1,1,9,9-tetrahydro-2,5-bistrifluoromethyl-3,6-dioxa-8-nonenol)(compound of the formula (7)) was not used, and 1,662 g of an aqueousdispersion of PFA having no functional group was obtained.

A concentration of the polymer in the aqueous dispersion was 9.7%, and aparticle size thereof was 115 nm.

A white solid was isolated in the same manner as in Reference Example 1,and analyzed.

TFE/PPVE=98.9/1.1% by mole Tm=310° C. 1% Thermal decompositiontemperature Td=479° C. Melt flow rate: 19.2 g/10 min

In infrared spectrum, no characteristic absorption of --OH was observed.

Reference Example 4

(Synthesis of PFA having hydroxyl)

A 6-liter glass-lined autoclave equipped with a stirrer, valve, pressuregauge and thermometer was charged with 1,500 ml of pure water. Afterreplacing with nitrogen gas sufficiently, the autoclave was evacuatedand charged with 1,500 g of 1,2-dichloro-1,1,2,2-tetrafluoroethane(R-114).

Then 5.0 g ofperfluoro-(1,1,9,9-tetrahydro-2,5-bistrifluoromethyl-3,6-dioxa-8-nonenol)(compound of the formula (7)), 130 g of perfluoro(propyl vinyl ether)(PPVE) and 180 g of methanol were fed into the autoclave withpressurized nitrogen gas, and a temperature inside the system wasmaintained at 35° C.

Pressurized tetrafluoroethylene (TFE) gas was introduced into theautoclave with stirring so that the inside pressure became 8.0 kgf/cm²G. Then 0.5 g of a 50% methanol solution of di-n-propylperoxydicarbonate was fed with pressurized nitrogen gas to initiate thereaction.

Since the pressure lowered with the advance of the polymerizationreaction, at the time when the pressure lowered down to 7.5 kgf/cm² G,it was increased again to 8.0 kgf/cm² by feeding tetrafluoroethylenegas, and the decreasing and increasing of the pressure were repeated.

With continuing supply of tetrafluoroethylene, every time when about 60g of tetrafluoroethylene gas was consumed after starting of thepolymerization, 2.5 g of the fluorine-containing ethylenic monomerhaving hydroxyl (compound represented by the formula (7)) was introducednine times (22.5 g in total) under pressure to continue thepolymerization. When about 600 g of tetrafluoroethylene was consumedafter starting of the polymerization, the supplying thereof wasterminated. The autoclave was cooled, and the un-reacted monomer andR-114 were released.

The obtained copolymer was washed, rinsed with methanol and thenvacuum-dried to give 710 g of a white solid. Components and theiramounts of the obtained copolymer which were determined through ¹⁹ F-NMRand IR analyses were TFE/PPVE/(Fluorine-containing ethylenic monomerhaving hydroxyl and represented by the formula (7))=97.0/2.0/1.0% bymole. In infrared spectrum, characteristic absorption of --OH wasobserved at 3,620 to 3,400 cm⁻¹. According to DSC analysis Tm was 305°C., and according to DTGA analysis 1% thermal decomposition temperatureTd was 375° C. A melt flow rate measured under conditions of preheatingat 372° C. for five minutes at a load of 7 kgf /cm² by using Koka-typeflow tester and nozzles of 2 mmφ×8 mm length was 32 g/10 min.

Reference Example 5

(Synthesis of PFA having no functional group)

Synthesis was carried out in the same manner as in Reference Example 1except thatperfluoro-(1,1,9,9-tetrahydro-2,5-bistrifluoromethyl-3,6-dioxa-8-nonenol)(compound of the formula (7)) was not used, and that 240 g of methanolwas used. Thereby 597 g of PFA having no functional group was obtained.

The obtained PFA was analyzed in the same manner as in Reference Example1.

TFE/PPVE=98.2/1.8% by mole Tm=310° C. Td=469° C. (1% decrease of weight)Melt flow rate: 24 g/10 min

Reference Example 6

(Preparation of powder coating composition of PFA having hydroxyl)

The PFA powder having hydroxyl and obtained in Reference Example 4(apparent specific gravity: 0.5, true specific gravity: 2.1, averageparticle size: 600 μm) was formed into a sheet of 60 mm wide×5 mm thickby compressing with Roller Compactor (model BCS-25 available from SINTOKOGIO, LTD.). Then the sheet was pulverized to about 10 mm diameter witha pulverizer, and further finely ground at 11,000 rpm at roomtemperature with a grinder (Cosmomizer Model N-1 available from NARAMACHINERY Co., Ltd.). Then coarse particles having a size of not lessthan 170 mesh (sieve opening: 88 μm) were removed with a classifier(High Bolder Model 300SD available from Shin-Tokyo Kikai KabushikiKaisha) to give a powder coating of PFA having hydroxyl. An apparentdensity of the powder was 0.7 g/ml, and an average particle size was 20μm.

Reference Example 7

(Preparation of powder coating composition of PFA having no functionalgroup)

A powder coating composition of PFA was prepared in the same manner asin Reference Example 6 except that the PFA powder (apparent specificgravity: 0.6, true specific gravity: 2.1, average particle size: 400 μm)having no functional group and obtained in Reference Example 5 was usedinstead of the PFA powder having hydroxyl and obtained in ReferenceExample 4. An apparent density of the powder was 0.73 g/ml, and anaverage particle size was 20 μm.

Reference Example 8

(Synthesis of fluorine-containing polymer by usingnon-fluorine-containing monomer having functional group)

A 1-liter stainless steel autoclave equipped with a stirrer, valve,pressure gauge and thermometer was charged with 250 g of butyl acetate,36.4 g of vinyl pivalate (VPi), and as a non-fluorine-containing monomerhaving hydroxyl, 32.5 g of 4-hydroxybutyl vinyl ether (HBVE) and 4.0 gof isopropoxycarbonyl peroxide. After cooling to 0° C. with ice andreplacing with nitrogen gas sufficiently, the autoclave was evacuatedand charged with 47.5 g of isobutylene (IB) and 142 g oftetrafluoroethylene (TFE).

With stirring, the autoclave was heated to 40° C., reaction was carriedout for 30 hours and then the reaction was terminated at the time whenthe inside pressure of the autoclave lowered down to lower than 2.0kg/cm². The autoclave was cooled and the un-reacted gas monomer wasreleased, and thereby a butyl acetate solution of a fluorine-containingcopolymer was obtained. A concentration of the polymer was 45%.

A fluorine-containing copolymer was taken out from the obtained butylacetate solution of a fluorine-containing copolymer throughreprecipitation method and isolated by sufficiently drying under reducedpressure. Elementary analysis of the obtained fluorine-containingcopolymer through ¹ H-NMR and ¹⁹ F-NMR indicated that the obtainedcopolymer was a copolymer of TFE/IB/VPi/HBVE=44/34/15/7% by mole.

Reference Example 9

(Synthesis of PFA having methyl ester group)

A 6-liter autoclave lined with glass and equipped with a stirrer, valve,pressure gauge and thermometer was charged with 1,500 ml of pure water.After replacing with nitrogen gas sufficiently, the autoclave wasevacuated and charged with 1,500 g of1,2-dichloro-1,1,2,2-tetrafluoroethane (R-114).

Then 2.7 g of methylperfluoro-(9,9-dihydro-2,5-bistrifluoromethyl-3,6-dioxa-8-nonenoate)(formula 8): ##STR9## 130 g of perfluoro(propyl vinyl ether) (PPVE) and220 g of methanol were fed into the autoclave with pressurized nitrogengas, and a temperature inside the system was maintained at 35° C.

Pressurized tetrafluoroethylene (TFE) gas was introduced into theautoclave with stirring so that the inside pressure became 8.0 kgf/cm²G.

Then 0.5 g of a 50% methanol solution of di-n-propyl peroxydicarbonatewas fed with pressurized nitrogen gas to initiate the reaction.

Since the pressure lowered with the advance of the polymerizationreaction, at the time when the pressure lowered down to 7.5 kgf/cm² G,it was increased again to 8.0 kgf/cm² by feeding tetrafluoroethylenegas, and the decreasing and increasing of the pressure were repeated.

With continuing supply of tetrafluoroethylene, every time when about 60g of tetrafluoroethylene gas was consumed after starting of thepolymerization, 2.7 g of the fluorine-containing ethylenic monomerhaving hydroxyl (compound represented by the formula (8)) was introducednine times (24.3 g in total) under pressure to continue thepolymerization. When about 600 g of tetrafluoroethylene was consumedafter starting of the polymerization, supplying thereof was terminated.The autoclave was cooled, and the un-reacted monomer and R-114 werereleased.

After washed and rinsed with methanol, the obtained copolymer wasvacuum-dried to give 710 g of a white solid. Components and theiramounts of the obtained copolymer which were determined through ¹⁹ F-NMRand IR analyses were TFE/PPVE/(Fluorine-containing ethylenic monomerhaving methyl ester group and represented by the formula(8))=97.8/1.0/1.2% by mole. In infrared spectrum, characteristicabsorption of --COOMe was observed at 1,795 cm⁻¹. According to DSCanalysis Tm was 308° C., and according to DTGA analysis 1% thermaldecomposition temperature Td was 376° C. A melt flow rate measured underconditions of preheating at 372° C. for five minutes at a load of 7kgf/cm² by using Koka-type flow tester and nozzles of 2 mmφ×8 mm lengthwas 29 g/10 min.

Reference Example 10

(Synthesis of PFA having carboxyl)

10 Grams of the white powder of PFA having a methyl ester group andobtained in Reference Example 9 was added to a mixed solvent comprising600 ml of methanol and 200 ml of water, in which 40 g of NaOH wasdissolved, followed by stirring at 70° to 75° C. for five hours.

After cooling, a 2N-HCl was added until pH of the solution became 2,followed by stirring for three hours.

A white powder was taken out, washed, rinsed with methanol and dried at100° C.

Through IR analysis, an absorption of carbonyl of carboxyl group and anabsorption of OH group were newly observed at 1,700 cm⁻¹ and 3,200 to3,700 cm⁻¹, respectively. According to DSC analysis Tm was 308° C., andaccording to DTGA analysis 1% thermal decomposition temperature was 335°C.

Reference Example 11

(Preparation of powder coating composition of PFA having methyl estergroup)

A powder coating composition having methyl ester group (apparentdensity: 0.71 g/l, average particle size: 20 μm) was prepared in thesame manner as in Reference Example 6 except that the PFA powder havingmethyl ester group and obtained in Reference Example 9 (apparentspecific gravity: 0.5, true specific gravity: 2.1, average particlesize: 650 μm ) was used instead of the PFA powder having hydroxyl andobtained in Reference Example 4.

Reference Example 12

(Preparation of powder coating composition of PFA having carboxyl)

A powder coating composition having carboxyl (apparent density: 0.73g/l, average particle size: 22 μm) was prepared in the same manner as inReference Example 6 except that the PFA powder having carboxyl andobtained in Reference Example 10 (apparent specific gravity: 0.52, truespecific gravity: 2.1, average particle size: 670 μm) was used insteadof the PFA powder having hydroxyl and obtained in Reference Example 4.

Example 1

(1) Pretreatment of substrate

A 1.5 mm thick pure aluminum plate (A1050P) and 1.5 mm thick SUS304 weredegreased with acetone, respectively.

(2) Formation of primer of fluorine-containing polymer having functionalgroup

The aqueous dispersion comprising the PFA having hydroxyl and preparedin Reference Examples 1 and 2 was applied with an air spray gun so thata coating thickness became about 5 μm, followed by infrared drying at90° C. for ten minutes and sintering at 380° C. for 20 minutes.

(3) Formation of layer (top layer) of fluorine-containing polymer havingno functional group

On the primer layer obtained in above (2) was coated with an aqueouscoating composition of PTFE (POLYFLON TFE ENAMEL EK4300CRN availablefrom Daikin Industries, Ltd.) as a coating composition comprising afluorine-containing polymer having no functional group, by using an airsprayer so that a coating thickness became about 20 μm, followed byinfrared drying at 90° C. for ten minutes and sintering at 380° C. for20 minutes.

(4) Evaluation of adhesion

A method for determining adhesion is mentioned below.

(Cross-cut adhesion test)

According to JIS K 5400 1990, 8.5.2, a coated surface is cross-cut togive 100 squares, an adhesive tape (available from Nichiban KabushikiKaisha) is adhered to the cross-cut surface tightly, and the tape istorn off. This is repeated ten times with new tapes to check to see howmany squares remain among 100 squares. The results are shown in Table 1.

Example 2

A coated plate was produced in the same manner as in Example 1 exceptthat a primer was formed by using the aqueous dispersion of PFA havinghydroxyl and obtained in Reference Example 2 as a fluorine-containingpolymer having functional group, and adhesion of the coating film wasevaluated in the same manner as in Example 1. The results are shown inTable 1.

Comparative Example 1

A coated plate was produced in the same manner as in Example 1 exceptthat a primer of the aqueous dispersion of PFA having no functionalgroup and obtained in Reference Example 3 was used instead of the primercomprising the fluorine-containing polymer having functional group, andadhesion of the coating film was evaluated in the same manner as inExample 1. The results are shown in Table 1.

Examples 3 and 4 and Comparative Example 2

Coated plates of Example 3, Example 4 and Comparative Example 2 wereproduced in the same manner as in Example 1, Example 2 and ComparativeExample 1, respectively except that a top layer was formed by using anaqueous coating of FEP (NEOFLON FEP Dispersion ND-1 available fromDaikin Industries, Ltd.) as a coating composition comprising afluorine-containing polymer having no functional group, and adhesion ofthe coating films were evaluated, respectively. The results are shown inTable 1.

Example 5

(1) Pretreatment of substrate

A substrate was pretreated in the same manner as in Example 1.

(2) Formation of primer layer of fluorine-containing polymer havingfunctional group

The aqueous dispersion comprising PFA having hydroxyl and prepared inReference Example 1 was applied with an air spray gun so that a coatingthickness became about 5 μm, followed by infrared drying at 90° C. forten minutes.

(3) Formation of layer (top layer) of fluorine-containing polymer havingno functional group

On the primer layer obtained in above (2) was coated with a powdercoating composition of PFA (NEOFLON PFA Powder Coating Composition ACX-3available from Daikin Industries, Ltd.) as a coating comprising afluorine-containing polymer having no functional group, throughelectrostatic coating so that a coating thickness became about 40 μm,followed by sintering at 380° C. for 20 minutes.

(4) Evaluation of adhesion

Adhesion was determined in the same manner as in Example 1.

The results are shown in Table 1.

Example 6

A coated plate was produced in the same manner as in Example 5 exceptthat a primer of the aqueous dispersion of PFA having hydroxyl andobtained in Reference Example 2 was used as a primer comprising afluorine-containing polymer having functional group, and adhesion of thecoating film was evaluated in the same manner as in Example 5. Theresults are shown in Table 1.

Comparative Example 3

A coated plate was produced in the same manner as in Example 5 exceptthat a primer of the aqueous dispersion of PFA having no functionalgroup and obtained in Reference Example 3 was used instead of the primercomprising the fluorine-containing polymer having functional group, andadhesion of the coating film was evaluated in the same manner as inExample 5. The results are shown in Table 1.

Example 7

(Evaluation of adhesion of PFA powder coating composition havinghydroxyl)

(1) Production of press sheet for adhesion test

About 4 g of the PFA powder coating composition having hydroxyl andprepared in Reference Example 6 was charged in a cylindrical die moldhaving a diameter of 60 mm, and compression-molded by using a pressmachine at room temperature at a pressure of 300 kgf/cm² to give adisc-like cold press sheet.

(2) Pretreatment of substrate

A 100×100×1 (mm) pure aluminum plate was sand-blasted after degreasedwith acetone.

(3) Production of adhered sample

The press sheet for test which was obtained in above (1) was placed onthe aluminum plate (above (2)), and put in a hot air dryer, heated andmelted at 330° C. for ten minutes. Thus a sample in which about 450 μmthick sheet was adhered to the aluminum plate was obtained.

(4) Measurement of adhesive strength

As shown in FIG. 1, the adhered sheet of the sample was cut at aninterval of 10 m with a cutter. One end of each strip-like sheet wasturned over and pulled up at an angle of 90° to the aluminum plate asshown in FIG. 2 to measure peel strength at room temperature at across-head speed of 50 mm/min by using Tensilon Universal Tester(available from Orientec Corporation). An adhesive strength was 5.5kgf/cm which was an average peeling load by area method.

Comparative Example 4

(Evaluation of adhesion of PFA powder coating composition having nofunctional group)

Production of a press sheet for an adhesion test, pretreatment of asubstrate and production of an adhered sample were carried out in thesame manner as in Example 7 except that the PFA powder coatingcomposition having no functional group and prepared in Reference Example7 was used instead of the PFA powder coating composition having hydroxyland prepared in Reference Example 6, to measure adhesive strength.

Adhesive strength of the PFA powder coating composition having nofunctional group was 0.8 kgf/cm.

Example 8

(Electrostatic coating of PFA powder coating composition havinghydroxyl)

The PFA powder coating composition having hydroxyl and prepared inReference Example 6 was subjected to electrostatic coating at roomtemperature at an applied voltage of 40 kV on the aluminum platepretreated in the same manner as in Example 7 by using an electrostaticcoating machine (Model GX3300 available from Iwata Toso KabushikiKaisha). The coated plate was sintered at 330° C. for 15 minutes in ahot air dryer to give a coating film.

The coating film was a transparent, uniform, continuous film and adheredto the aluminum plate strongly.

Comparative Example 5

(Thermal resistance of fluorine-containing polymer prepared by usingnon-fluorine-containing monomer having functional group)

A thermal decomposition temperature of the fluorine-containing copolymerobtained in Reference Example 8 was measured through TGA analysis, and1% thermal decomposition temperature thereof was 220° C. It wasrecognized that the fluorine-containing copolymer prepared by using anon-fluorine-containing monomer having functional group as in ReferenceExample 8 has low thermal resistance.

Further the fluorine-containing copolymer prepared in Reference Example8 was dissolved in butyl acetate in a concentration of 10% by weight.

Then pretreatment of a pure aluminum substrate, coating of a primerlayer of the fluorine-containing polymer of Reference Example 8 andcoating of a top layer (electrostatic coating of a PFA powder coatingcomposition) were carried out in the same manner as in Example 5 exceptthat the butyl acetate solution containing the fluorine-containingpolymer of Reference Example 8 was used instead of the aqueousdispersion of PFA having hydroxyl which was used for the primer layer.

The coating film obtained by sintering at 380° C. for 20 minutes wascolored brown and foamed, and also separation was seen. Thus uniformtransparent coating film could not be obtained.

                                      TABLE 1                                     __________________________________________________________________________                   Ex. 1                                                                              Ex. 2                                                                              Com. Ex. 1                                                                          Ex. 3                                                                              Ex. 4                                                                              Com. Ex. 2                                                                          Ex. 5                                                                              Ex. 6                                                                              Com. Ex.             __________________________________________________________________________                                                             3                    Fluorine-containing aqueous                                                                  Ref. Ex. 1                                                                         Ref. Ex. 2                                                                         Ref. Ex. 3                                                                          Ref. Ex. 1                                                                         Ref. Ex. 2                                                                         Ref. Ex. 3                                                                          Ref. Ex. 1                                                                         Ref. Ex. 2                                                                         Ref. Ex. 3                                                                     dispersion used                                                              for primer layer       Fluorine-containing resin PTFE PTFE PTFE FEP FEP FEP PFA PFA PFA                                                                      forming top                                                                  layer                  Evaluation of adhesion                                                        (Cross-cut adhesion test)                                                     SUS304 100/100 100/100 0/100 100/100 100/100  0/100 100/100 100/100                                                                  20/100                 Pure aluminum 100/100 100/100 0/100 100/100 100/100 20/100 100/100                                                                   100/100 30/100       __________________________________________________________________________

INDUSTRIAL APPLICABILITY

According to the fluorine-containing coating material and the coatingmethod of the present invention, coated articles having excellentadhesion can be obtained for surfaces of various substrates havingvarious shapes. Also excellent thermal resistance, chemical resistance,non-sticking property, low friction property, and electrical and opticalproperties of the fluorine-containing polymer can be given to thesubstrates, thus making it possible to be available for variousapplications.

By applying the fluorine-containing coating material of the presentinvention through the coating method of the present invention, corrosionresistance, rust preventing property, chemical resistance, weatherresistance, non-sticking property and sliding property can be given tometal surfaces, for example, aluminum, iron, alloys, etc., thus makingit possible to be available for various applications such as buildingmaterial, chemical plant, food processing, cooking apparatus,car-related parts, OA-related parts, etc.

For surfaces of copper and copper-containing metals, excellentelectrical properties of a fluorine-containing resin (particularly highfrequency electric insulation) can be given, thus enabling applicationsin the electrical and electronic fields such as printed circuit boardsand electrical and electronic parts for high frequency.

For surfaces of glass materials, water-repelling property, oil-repellingproperty, anti-reflection property and low refraction can be givenwithout losing transparency, which makes it possible to use the coatedglass materials for optical parts, liquid crystal-related parts, glassfor building and glass for cars. Also a function to prevent glasses frombroken can be exhibited, which makes it possible to use the coated glassfor instruments for illumination and explosion-proof glass for building.

What is claimed is:
 1. A resin composition for a fluorine-containingcoating composition which comprises:(A-1) 1 to 90% by weight of afluorine-containing ethylenic polymer having a functional group andprepared by copolymerizing (a-5) 0.05 to 30% by mole of at least one offluorine-containing ethylenic monomers having any one of functionalgroups selected from the group consisting of hydroxyl, carboxyl,carboxylate salt group, carboxylate ester group and epoxy and (b-5) 70to 99.95% by mole of at least one of fluorine-containing ethylenicmonomers which do not have the functional group mentioned above and,(B-1) 10 to 99% by weight of a fluorine-containing ethylenic polymerhaving no functional group in a branched chain.
 2. The resin compositionfor a fluorine-containing coating composition of claim 1, wherein thefluorine-containing polymer (A-1) having a functional group is at leastone of fluorine-containing ethylenic polymers having a functional groupselected from the group consisting ofa copolymer of (a-5) at least oneof the fluorine-containing ethylenic monomers having a functional groupand represented by the formula (1):

    CX.sub.2 ═CX.sup.1 --R.sub.f --Y                       (1)

wherein Y is a --CH₂ OH, --COOH, carboxylate salt group, carboxylateester group or epoxy, X and X¹ are the same or different and each ishydrogen atom or fluorine atom, R_(f) is a divalent fluorine-containingalkylene group having 1 to 40 carbon atoms, a fluorine-containingoxyalkylene group having 1 to 40 carbon atoms, a fluorine-containingalkylene group having an ether bond and 1 to 40 carbon atoms or afluorine-containing oxyalkylene group having an ether bond and 1 to 40carbon atoms, and (b-5) tetrafluoroethylene and a copolymer of (a-5) thefluorine-containing monomer defined above having a functional group and(b-5) a monomer mixture of 85% to 99.7% by mole of tetrafluoroethyleneand 0.3 to 15% by mole of a monomer represented by the formula (3):

    CF.sub.2 ═CF--R.sub.f.sup.3                            ( 3)

wherein R_(f) ³ is --CF₃ or OR_(f) ⁴, in which R_(f) ⁴ is aperfluoroalkyl group having 1 to 5 carbon atoms, said % by mole beingbased on the total amount of the monomers excepting (a-5) and (B-1) isat least one of the polytetrafluoroethylene,tetrafluoroethylene-hexafluoropropylene copolymer ortetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer.